es were less than 10 s.
Comparing pressure resistance of organisms associated with
ranch spoilage. Ranch dressing was prepared as described previously, then P. acidilactici, L. brevis, and T. delbrueckii were inoculated individually in the product. Inoculation levels were 105 CFU
T. delbrueckii per gram and 107 CFU per gram for each bacterial
strain. Bags of inoculated dressing (50 g each) were pressure treated
at 200, 400, or 600 MPa with a holding time of 3 min, then survivors
were determined as described subsequently. Controls were bags of
uninoculated dressing and inoculated but not pressure-processed
dressing. Sample bags were stored at 26 ◦C for 2 wk, observed visually for gas production every 2 d, and microbiologically analyzed on
days 7 and 14 of storage. For microbial analyses, dressing samples
were initially diluted in a 1:1 (w/v) ratio of ranch dressing and 0.1%
peptone water to obtain a slurry that could be easily pipetted while
maintaining a reasonable detection limit. This initial dilution was
followed by decimal dilutions in 0.1% peptone water, and spreadplating on appropriate media (MRS agar or RDA). Recovery of inoculated strains was verified by examining growth on agar plates for
colony and cell morphology and the Gram-reaction.
es were less than 10 s.Comparing pressure resistance of organisms associated withranch spoilage. Ranch dressing was prepared as described previously, then P. acidilactici, L. brevis, and T. delbrueckii were inoculated individually in the product. Inoculation levels were 105 CFUT. delbrueckii per gram and 107 CFU per gram for each bacterialstrain. Bags of inoculated dressing (50 g each) were pressure treatedat 200, 400, or 600 MPa with a holding time of 3 min, then survivorswere determined as described subsequently. Controls were bags ofuninoculated dressing and inoculated but not pressure-processeddressing. Sample bags were stored at 26 ◦C for 2 wk, observed visually for gas production every 2 d, and microbiologically analyzed ondays 7 and 14 of storage. For microbial analyses, dressing sampleswere initially diluted in a 1:1 (w/v) ratio of ranch dressing and 0.1%peptone water to obtain a slurry that could be easily pipetted whilemaintaining a reasonable detection limit. This initial dilution wasfollowed by decimal dilutions in 0.1% peptone water, and spreadplating on appropriate media (MRS agar or RDA). Recovery of inoculated strains was verified by examining growth on agar plates forcolony and cell morphology and the Gram-reaction.
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